However doctors say it's important to look at the other adults who showed no signs of ADHD.

Mike Manos, PH.D./Cleveland Clinic said, "It would be fascinating and necessary now, to take a look at the cohort that adapted and find out what is it that they did that made their symptoms non-persistent? That made their symptoms non-problematic. That made them successful as adults."

The study also found more than half of the adults who had childhood ADHD now had another psychiatric disorder.